Semiconductor integrated circuits are known in the art. Typically, integrated circuits include a package which contains one or more substrates or “dies”. The substrates may be provided with electronic circuits and be provided with pads via which the substrates (and the electronic circuits) can be connected to the outside world, e.g. via bond-wires that are connected to pins which extend from the package inside to the exterior of the package.
However, a general problem is that current may be injected into the substrate, for example when a pad is driven below or above the supply voltage, which may affect the operation of the electronic circuit.
In order to prevent the injected current from affecting the operation, it is known to implement a so called “guard ring” which shields the electronic circuit from the injected current. For example, U.S. Pat. No. 5,168,340 describes a passive latch-up protection improvement in which polysilicon lines cross or cut a guard-ring around a logic circuit. When an amount of injected current exceeds a certain magnitude, latch up of the transistors in the logic circuit occurs and the transistors are shut off.